1. Field of the Invention
The present invention relates to an image forming apparatus that has a positively-charged single layer type electrophotographic photoreceptor and a contact charging member.
2. Description of the Related Art
A negatively-charged multilayered photoreceptor and a positively-charged single layer type photoreceptor are known as photoreceptors of an eletrophotographic image forming apparatus. Among these, the positively-charged single layer type photoreceptor is designed to last long because its film thickness can be increased relatively easily. In addition, compared to the multilayered photoreceptor, the single layer type photoreceptor can be produced more easily at a lower cost since it requires only a coating process for a single layer.
Furthermore, in consideration of the environment, a contact charging system that performs, for example, roller charging using a rubber roller has been widely used in the electrophotographic image forming apparatuses, as an alternative to a scorotron charging system (non-contact system) that generates a large amount of ozone. This roller charging where a photoreceptor is charged by discharge in a small gap between the photoreceptor and a roller realizes a reduction of the ozone.
It is considered that an environmentally responsive electrophotographic image forming apparatus can be designed by a combination of a single layer type photoreceptor and the roller charging. However, although the contact charging system that produces less ozone is widespread in the market in the field of a system using a negatively-charged multilayered photoreceptor, the conventional scorotron charging system has still been used in a system using a positively-charged single layer type photoreceptor that produces less ozone as compared to the negatively-charged multilayered photoreceptor.
As environmental awareness increases in recent years, however, the amount of ozone that is discharged by the scorotron charging system in the system using the positively-charged single layer type photoreceptor is not acceptable in the market. For this reason, the system using the positively-charged single layer type photoreceptor also needs to employ the contact charging system.
In addition, increasing the life-span of a photoreceptor leads to a reduction in wastes, which is also highly desired in the market. However, employing the contact charging system facilitates peeling of a film of the photoreceptor, reducing the life-span of not only the photoreceptor but also a contact charging member by half.